r - case_when in mutate pipe

Question

It seems dplyr::case_when doesn't behave as other commands in a dplyr::mutate call. For instance:

library(dplyr)

case_when(mtcars$carb <= 2 ~ "low",
          mtcars$carb > 2 ~ "high") %>% 
  table

works:

.
high  low 
  15   17 

But put case_when in a mutate chain:

mtcars %>% 
  mutate(cg = case_when(carb <= 2 ~ "low",
                        carb > 2 ~ "high"))

and you get:

 Error: object 'carb' not found

while this works fine

mtcars %>% 
  mutate(cg = carb %>% 
           cut(c(0, 2, 8)))

Answer 1

As of version 0.7.0 of dplyr, case_when works within mutate as follows:

library(dplyr) # >= 0.7.0
mtcars %>% 
  mutate(cg = case_when(carb <= 2 ~ "low",
                        carb > 2  ~ "high"))

For more information: http://dplyr.tidyverse.org/reference/case_when.html